This application claims the priority benefit of Japan application serial no. 2001-126909, filed Apr. 25, 2001.
The present invention relates to a panel used for a color cathode ray tube
Glass parts for a color cathode ray tube as shown in FIG. 4, includes a panel 1 on which an image is displayed, and a funnel 3 in an approximately funnel shape comprising a neck portion 2 for inserting an electron gun.
The panel 1 and the funnel 3 are sealed to each other through a frit glass 5 interposed between respective seal end surfaces 4 of the panel 1 and the funnel 3 opposing to each other The sealing is conducted as follows The funnel 3 is held while the seal end surface 4 thereof is facing up The crystalline frit glass in a slurry state mixed with an organic binder (so-called vehicle) is applied on the seal end surface 4. After the frit glass is dried, the panel 1 is placed on the funnel 3 while the seal end surface 4 thereof is facing down. The frit glass is then heated and sintered.
A fluorescence screen and a shadow mask required for displaying an image are applied on an inner surface of the panel for a color cathode ray tube. Because the panel and the funnel are sealed to each other after the fluorescence screen and the shadow mask are applied on the inner surface of the panel, flaws tend to be generated, and organic matters, carbon powders, and iron powders tend to attach on the seal end surface of the panel in a manufacturing process and transporting and packaging in the manufacturing process. If the panel and the funnel are sealed to each other while flaws or dirt are present on the seal end surfaces thereof, the sealed portion cannot have a desired strength As a result, the cathode ray tube does not present a desired strength or performance.
Namely, when the panel is transported in the manufacturing process while the seal end surface thereof is facing down, flaws tend to be generated as a result of a contact and a friction between the seal end surface thereof and a transport device. Especially, when a so-called penetration flaw, which is present across the seal end surface in the widthwise direction, is generated, and the frit glass does not completely penetrate into the penetration flaws in the process for sealing the panel and the funnel to each other, a vacuum leak occurs at the penetration flaws in the cathode ray tube When dirt is attached to the seal end surface, the dirt remains in the sealed portion as a conductive foreign material, and causes a dielectric breakdown in a following process for manufacturing the cathode ray tube. The organic matter is carbonized, and the metal component is unchanged or oxidized when they are exposed to a high temperature atmosphere at more than 400xc2x0 C. in the process for sealing the panel and the funnel to each other or in an evacuation process for the glass bulb As a result, both of them remain as conductive foreign materials When a high voltage is impressed on a cathode ray tube using such glass bulb as sealed in this state, an electric field concentration may occur at the sealed portion, and may cause a breakage of the cathode ray tube.
In view of the foregoing, it is necessary to handle the seal end surface of the conventional panel with a special care.
It is preferable to mirror-finish the seal end surface of the panel in terms of preventing dirt from attaching. On the other hand, the seal end surface tends to be flawed, and to generate a penetration flaw described before. In addition, when the seal end surface is mirror-finished, there are defects such as decreased releasability of the panel from the mold after press-molding, increased possibility of seizure of glass to the mold surface, and increased time and cost of manufacturing processes such as grinding and polishing after molding.
For example, Japanese Patent Laid-Open Publication No Hei 11-40081 proposes a rough seal end surface of a panel as a measure for removing dirt and preventing flaws on the seal end surface of the panel However, since recesses and protrusions constituting the rough surface still tend to catch dirt on the seal end surface of the panel, and a large number of recesses and protrusions are randomly formed, when dirt once attached to the seal end surface has to be removed, it is difficult to sufficiently remove the dirt penetrated into the recesses Thus, the problem that the dirt tends to remain till later still survives.
An object of the present invention is to provide a panel for a color cathode ray tube having the following characteristics The panel has a seal end surface to which dirt hardly attaches, and from which dirt once attached is removed easily The seal end surface hardly generates a penetration flaw. The panel is able to obtain a desired seal strength using a frit glass, does not decrease manufacturing yield, and attains high productivity.
To attain the object above, the present invention provides a panel for a color cathode ray tube comprising an opening portion including a seal end surface, the seal end surface being to be sealed to a funnel through a frit glass, wherein the seal end surface of the opening portion is a rough surface comprising a large number of streak-shape ridges and troughs in which minute recesses and protrusions range in a circumference direction of the seal end surface Where the expression xe2x80x9cminute recesses and protrusions range in a circumference directionxe2x80x9d means that each of the ridges and each of the troughs themselves are minutely uneven in the circumference direction, respectively.
With the constitution above, because the seal end surface of the opening portion is the rough surface comprising the large number of the streak-shape ridges and the troughs in which the minute recesses and protrusions range in a circumference direction of the seal end surface, dirt hardly attaches to the seal end surface Because the ridges and the troughs are formed in the circumference direction of the seal end surface, wiping along the circumference direction of the seal end surface easily removes dirt once attached. Also, because the seal end surface is a rough surface, the area of contact thereof is small Thus, when the panel, for example, is transported while the seal end surface is facing down, flaws are hardly generated on the seal end surface. Because the large number of the streak-shape ridges exist, even if flaws are generated, the generation of the aforementioned penetration flaws in the widthwise direction of the seal end surface, which causes a vacuum leak of the cathode ray tube, is prevented.
Further, the frit glass tends to easily flow in the circumference direction of the seal end surface in a process for sealing the panel to the funnel Thus, filling of the frit glass into the respective recesses of the minute recesses and protrusions, which range in the circumference direction for constituting the ridges and the troughs, is promoted as well As a result, high seal strength is provided.
The streak-shape ridges and the streak-shape troughs may be continuous or intermittent as far as they are formed along the circumference on the seal end surface.
In the constitution above, it is preferable that the streak-shape ridges and troughs are formed on a surface occupying 20% or more of the seal end surface in a widthwise direction, 0.5 xcexcm less than Rz less than 5.0 xcexcm is satisfied where Rz (xcexcm) is ten-point height of roughness profile, that is, ten-point average roughness of the recesses and the protrusions of the ridges and the troughs in the widthwise direction of the seal end surface, and 100xe2x89xa6Sm/Rzxe2x89xa6500 is satisfied where Sm (xcexcm) is mean width of the profile elements, that is, an average interval between the recesses and the protrusions.
The depth of the recesses and protrusions of the ridges and the troughs in the widthwise direction on the seal end surface, and the interval between the recesses and the protrusions with respect to the depth of the recesses tend to affect the easiness for removing attached dirt When Rzxe2x89xa75.0 xcexcm or Sm/Rz less than 100, the depth of the recesses and protrusions of the ridges and the troughs tends to become too deep, also the interval between the recesses and the protrusions with respect to the depth of the recesses, namely the interval between the ridges and the troughs, tends to become too narrow. On the other hand, when Rzxe2x89xa60.5 xcexcm or Sm/Rz greater than 500, the releasability of the panel from the mold after the press-molding tends to decrease, so that the seizure of the glass to the mold surface tends to occur With the constitution above, the depth of the recesses and protrusions of the ridges and the troughs in the widthwise direction of the seal end surface of the panel does not become too deep, and the interval between the recesses and the protrusions with respect to the depth of the recesses does not become too narrow. Thus, it is possible to prevent dirt from attaching the seal end surface and to remove attached dirt more easily. In addition, the releasability of the panel from the mold, and the prevention of the seizure of the glass to the surface of the mold further increase in the process for molding the glass panel.
To stably provide these effects, it is especially preferable to form the ridges and troughs on a surface occupying 20% or more of the seal end surface in the width wise direction.
When the seal end surface is left as a surface formed by press-molding in the constitution above, a generation of minute flaws caused by grinding, polishing and the like are avoided on the glass This is more preferable in terms of maintaining original strength of the glass forming the panel, and contributes to increasing the productivity as well.
There is a following easy method for forming the rough surface on the seal end surface of the panel of the present invention when the seal end surface is left as a surface formed by press-molding A grinding wheel, abrasive grains, sand paper or the like is used to apply a grinding operation along the circumference direction on a part of a mold for the panel, which molds the seal end surface of the panel, to form a large number of streak-shape ridges and troughs on the mold in which minute recesses and protrusions range. These streak-shape ridges and troughs on the mold are transferred on the seal end surface of the panel during press-molding. For example, the large number of streak-shape ridges and troughs, in which the minute recesses and protrusions range, are properly forms by sliding a jig, which is formed by implanting abrasive grains such as diamond or alundum on a metal rod or a metal plate In forming of the rough surface on the seal end surface by transferring from the mold, the state of the rough surface transferred on the glass surface is slightly more rounded and smoother than the state of the rough surface formed on the mold. As a result, removing dirt becomes easier